The present invention relates generally to black body calibration targets. In particular, black body calibration targets comprising black silicon.
Instruments require calibration. Optical instruments are typically calibrated using a calibration target. To calibrate optical thermal imaging systems accurately, a blackbody calibration source may be employed by placing a blackbody calibration target at one or more known temperatures within the optical path of the instrument, measuring the temperature of the calibration target at the various temperatures, and calibrating the instrument according to these measurements. Accurate calibration requires accurate determination of temperatures within a number of micro-Kelvin or below. However, most materials exhibit some emissivity, which is the measure of an object's ability to emit infrared and other wavelengths of energy. Emitted energy relates to the temperature of the object using the Planck law. Emissivity can have a value from 0 (e.g., a shiny mirror) to a theoretical value of 1.0, in which no extraneous electromagnetic radiation is reflected, which is a perfect blackbody.
Blackbodies known in the art utilize a temperature controlled substrate which is coated with a relatively high emissivity paint or other coating having an emissivity typically on the order of 0.9. Known blackbodies are often shaped to further limit the emissivity of the calibration target, resulting in a blackbody calibration source having an average emissivity on the order of 0.92-0.93 over a particular wavelength range. Blackbody calibration sources known in the art, however, are prone to mechanical fatigue, i.e., the coating flakes off of the substrate, the substrate becomes contaminated with materials, and the like. In addition, commercially available blackbody systems typically include a three dimensional well of substantial size and mass oriented to prevent reflection of incoming electromagnetic radiation. Such known blackbodies are often large, bulky assemblies with complicated optics and geometries. Employment of blackbodies in situations where space and mass are limited, such in spacecraft and miniaturized instruments is problematic in the art.
Blackbodies are essential to numerous facets of future space missions. The accurate calibration enables lower level raw data products from spacecraft sensors to be transitioned into meaningful, higher level products and information. Accurate blackbodies form the basis for relating raw data acquired by the instruments back to a standard metric. Likewise, as spacecraft and instruments continue to decrease in size, smaller and smaller blackbody calibrations sources are required. In addition, mass is always a primary concern in spacecraft.
There is a long felt need in the art for robust blackbody calibration targets with decreased size and mass, with improved emissivity over coated substrates.